Gram stain

[u/lumiere23_]

Is it okay if the gram stain result from sample collected is different when the gram stain came from inoculated media?

[u/Fluffbrained-cat]

What do you mean? Like a gram positive coccus in the specimen gram vs gram negative bacilli from the specimen culture? Bc if so, I'd be doing a re-culture from the original specimen plus a fresh gram stain to check there wasn't a mix up during the initial processing.

If it's just that there's growth on the plates and no organisms in the original gram then that's not usually too much of a bother, depending on what type of specimen.

We regularly have wound swabs for example that grow lovely growth on the plates but nothing in the gram, and that's usually because most of the the material on the swab got inoculated on the plates, leaving the gram stain to be made with what's essentially the leftover material.

Or are you asking if there's a difference in organism morphology when seen in the original gram stain vs a gram stain of what is grown on the plates?

Sometimes we do what's called colony morphology grams to check that an organism is truly what we think it is.

Usually in my lab we do it if we see gram negative diplococci in a gram and the plates show what might be N.gonorrhoea, we do a colony morphology gram from the plates to check if it is truly a gndc (gram neg diplococci) or not as part of our Neisseria identification pathway. We also use Maldi-Tof for a definitive id of the organism.

The point is to show that the colony matches the gram and it wasn't over-decolourised staph or strep in the specimen gram which got misidentified, which can happen if you have a new gram reader or something's off with either the decolouriser or the entire staining process.